If velocity is relative and dependent on an observer then how does an isolated object "approach the speed of light"? Approaching the speed of light relative to what??? Does the ubiquitous constant velocity/closed compartment analogy break down at relativistic speeds? If one were traveling "near the speed of light" and stopped accelerating, what is different about that scenario and any other of constant velocity? I.e. who's to say that 'you' aren't moving at near light speed away from 'me' and not the other way around? In reality, I think both perspectives may be correct, but if that's so, then why is a near infinite amount of energy required to accelerate further after 'I' have returned to a state of constant velocity 'near the speed of light'? Why doesn't it also take a near infinite amount of energy for 'you' (who we took to be stationary at the start of this exercise) to accelerate in the direction opposite of me? These questions all really boil down to the same central conundrum. If all constant velocity motion is relative, then how does the concept of velocity have any meaning at all???